1. Field of the Invention
The invention concerns a hydraulic line connection with a supply connection having a pressure line and a return line, each ending at a connection valve, and with a safety valve in a line between the pressure line and a consumer, said safety valve having a valve element, whose one side is acted upon by the pressure at the pressure connection with the purpose of opening.
2. Description of the Related Art
A hydraulic line connection of this kind is, for example, used when a hydraulic auxiliary equipment must be detachably connected with the hydraulic pressure source. An example of this is farming machinery, which can be connected with the hydraulic system of a tractor. As the tractor uses different working machines in dependence of the task to be solved, such a hydraulic line connection, which is usually made as a snap connection, is required.
Until now, snap connections with connection valves have been used for this kind of hydraulic line connections. The connection valves close the line, when the line connection is separated. This usually happens by pulling a connection plug out of a connection socket or vice versa. Thus, hydraulic fluid is prevented from escaping from the system.
This embodiment has, however, a disadvantage. When, for example, the pressure line is connected correctly, so that the corresponding connection valve here opens, however, the connection valve on the return line does not open, as the return line is not, or is not correctly, connected with the tractor, the pressure will be built up of the pressure connection in the working machine. In unfavourable cases, this can lead to an overload, and even to a damaging of hydraulic elements in the working machine. For example, proportional valves may be damaged.
To reduce this problem, DE 38 16 987 C1 discloses the arrangement of a safety valve in the line connection. This valve has a slide, which, in its resting position, cuts the connection between the pump connection and the working machine, while creating a connection to the tank instead. In the working position, however, a connection between the pump line and the working machine is enabled. From one front side this slide is acted upon by the pressure in the pressure line, from the other front side by the same pressure and additionally by the force of a spring. To be able to move the slide in its working position, it is necessary to mechanically open a non-return valve, which is arranged between this front side and the tank line. For this purpose, the snap connection is used, with which the tank line connects the working machine with the tractor.
A solution of this kind is relatively expensive. It requires a relatively accurate production, to make sure that the non-return valve opens and closes reliably. The mechanical elements may wear off, which may influence the function safety of the safety valve.
The invention is based on the task of providing a simple production of a hydraulic line connection.
In connection with a hydraulic line connection as described in the introduction, this task is solved in that the other side of the valve element is directly connected with the return line.
With this embodiment, initially the pressure of the pressure line acts upon both sides of the valve element. In the closing direction, a spring is also acting. Somehow, for example via the consumer, the pressure on the closing side comes from the pressure line into the return line, so that firstly the valve element is closed by the effect of the spring and remains in this position. To open, however, it is only necessary to reduce the pressure in the return line. Such a reduction also appears automatically, when the connection valve of the return line is opened. However, this is only the case, when the corresponding connection is connected correctly. Thus, the operation of an additional element is saved. Nevertheless, it is ensured that the pressure from the pressure line can only act upon the consumer, when the return line is correctly connected, that is, a connection from a pressure sink, for example a tank, has been established. In the present case, the term xe2x80x9cdirectlyxe2x80x9d merely means that a pressure reduction at the connection valve can without problems propagate to the other side of the valve element through the return line. Thus it is indeed permissible, for example, to mount non-return valves in the return line, which open away from the valve element. Such valves do not influence the function.
Preferably, a throttle is provided between the pressure and the return line. Thus, a defined path for the pressure from the pressure line to the return line is created. Thus, the consumer is safely protected in all cases. When the pressure line is connected, the safety valve closes until the pressure in the tank line decreases.
Preferably, the throttle is arranged in the valve element. This permits a very simple embodiment of the safety valve.
It is preferred that the throttle is closed in the opening position of the valve element. This prevents a leakage between the pressure connection and the return line. Here the particular advantage of the placing in the valve element appears. When the valve element is opened, the change of its position enables it to close the throttle simultaneously.
Preferably, the valve element is made in the shape of a slide. This is a very simple embodiment. The slide can simply be moved back and forth. In its closing position it can, for example, with an area near the front side, bear on an edge, which then forms the desired sealing zone.
Preferably, the surface of the valve element, upon which the pressure acts in the opening direction, expands on opening the valve. This is, for example, reached in that the slide in the area of the end, in which the pressure connection ends, has a circumferentially bevelled edge. This edge then forms a surface, with which the slide bears on a housing edge, which forms a valve seat. As long as the valve element is closed, only a relatively small pressure acts in the opening direction, so that the pressure in the closing direction can be kept at a limited level. When the pressure in the closing direction is limited, however, it can also be reduced faster, so that the reaction time of the valve can be kept relatively small. As soon as the slide has made a small opening movement, the pressure reaches its whole front side and accordingly acts upon the slide in the opening direction. A slight increase in the pressure in the closing direction, which often appears, is then insignificant.
Advantageously, the consumer produces a counter pressure, which is larger than the pressure required to open the safety valve. Thus, the safety valve remains open after the first opening, until the hydraulic connection is released or the pressure in the pressure line drops, for example, when the pump is turned off.
Preferably, the consumer has an inlet module, which produces the counter pressure. Otherwise, the consumer can be relieved of this task.
In a preferred embodiment it is provided that the consumer connection has a valve bridge, which is formed by two pairs of non-return valves, opening in the same direction and being arranged in series between the pressure line and the return line, the middle outlets of each pair being connected with a connection valve. This valve bridge is comparable with an electrical rectifier, which is made as a xe2x80x9cWheatstonexe2x80x9d bridge. The valve bridge protects against an exchange of the two connection valves, that is, no harm will be done, when the connection valve belonging to the pressure line is connected with the tank line and vice versa.